In order to drive a vehicle, a construction machine, an industrial machine, and the like, a fluid circuit in which a pressure fluid such as hydraulic pressure flows into a cylinder to move a piston and drive a load is conventionally used. In accordance with an operation of returning the piston, the pressure fluid discharged from the cylinder is also stored in an accumulator so as to collect energy of the pressure fluid.
As an example of such a fluid circuit, one example of a hydraulic circuit shown in Patent Citation 1 will be described. With reference to FIG. 10, the hydraulic circuit is mainly formed by a drive mechanism 1, a hydraulic pump 2 for a main circuit, a hydraulic pump 3 for a pilot circuit, a direction switching valve 4, a cylinder device 5, a hydraulic remote controller valve 6, an electromagnetic switching valve 26, an accumulator 27 and a controller 28.
When an operation lever 6-1 of the hydraulic remote controller valve 6 is operated in the contracting direction C and the switching valve 4 is switched to a contracting position 4C, pressure oil from the pump 2 flows into a first oil chamber 5-1 of the cylinder device 5, and oil in a second oil chamber 5-2 passes through an oil passage 23 and is discharged to a tank 11 via the switching valve 4. At this time, an electric signal from a pressure sensor 10 is inputted to the controller 28, the electromagnetic switching valve 26 is switched to an accumulating position 26C, and part of discharge oil of the oil passage 23 passes through an oil passage 30 and is accumulated in the accumulator 27.
When the operation lever 6-1 of the hydraulic remove controller valve 6 is operated in the extending direction E, the switching valve 4 is switched to an extending position 4E, the pressure oil from the hydraulic pump 2 passes through oil passages 12, 15, 23 and flows into the second oil chamber 5-2 of the cylinder device 5, and the oil in the first oil chamber 5-1 is discharged to the tank 11 via the switching valve 4. At this time, an electric signal from a pressure sensor 9 is inputted to the controller 28, the electromagnetic switching valve 26 is switched to a pressure releasing position 26E, and the accumulated oil in the accumulator 27 passes through the oil passages 30, 29, joins the oil passage 23, and is supplied to the second oil chamber 5-2 of the cylinder device 5, that is, regenerated. At the same time, by an electric signal from the controller 28, drive force of the drive mechanism 1 is reduced. Thereby, in comparison to a case where there is no accumulator 27, similar cylinder extension speed can be obtained while reducing power of the drive mechanism 1. As a result, energy saving of the system can be achieved.